The pain continues, after finding water between the inner liner and the hull in my 1972 Skipjack 20 open, I looked everywhere but could not find the source of the water. But it was fresh water. I thought it might be coming from the fish hold, but no. I ended up pulling the gas tank so I could see everything, now I could get under the engine and look for any kind of hole or crack, this is what I discovered:
The motor mount bolts had rusted out, not completely but one was loose letting water go from the bilge to the hull through the hole in the stringer. Quite a bit of water in fact. And of course the hole had some rot.
After reading other posts on this topic and after freaking out I pulled the motor, now I could see the entire problem. These motor mounts are just screwed into the stringers using steel lag bolts, not stainless bolts. In fact, all the bolts on all 4 mounts were rusted somewhat. But the one by the transom was pretty bad. Not even any silicone! Maybe they didn't make it in 1972 when they made my boat.
So here is how I solved the problem, I'm only posting to possibly help someone else with the same problem. I had to drill a bunch of exploratory holes, both vertically and horizontally in the stringers to find the extent of the rot. The rot was only in one motor mount but in 2 holes. So I let the whole thing dry out for a month, then drilled 1/2 holes in the rotted sections and poured epoxy in. I did some quick calculations, turns out the thrust force on the prop can be over 2000 lbs at 150 hp. This also means the front motor mounts are being pushed up and the rear down. So I came up with a system of 5 vertical and 6 horizontal lag bolts to hold each motor mount, and I fabricated some "tee" style mounts out of aluminum plate.
Then I used two tubes of 3M 5200 to hold everything in place and I installed the mounts, they are shown below. Yes it is overkill and yes I spent too much pulling the motor, making the mounts etc but now I have piece of mind, at least when it comes to this (one of many) problem.
The motor mount bolts had rusted out, not completely but one was loose letting water go from the bilge to the hull through the hole in the stringer. Quite a bit of water in fact. And of course the hole had some rot.
After reading other posts on this topic and after freaking out I pulled the motor, now I could see the entire problem. These motor mounts are just screwed into the stringers using steel lag bolts, not stainless bolts. In fact, all the bolts on all 4 mounts were rusted somewhat. But the one by the transom was pretty bad. Not even any silicone! Maybe they didn't make it in 1972 when they made my boat.
So here is how I solved the problem, I'm only posting to possibly help someone else with the same problem. I had to drill a bunch of exploratory holes, both vertically and horizontally in the stringers to find the extent of the rot. The rot was only in one motor mount but in 2 holes. So I let the whole thing dry out for a month, then drilled 1/2 holes in the rotted sections and poured epoxy in. I did some quick calculations, turns out the thrust force on the prop can be over 2000 lbs at 150 hp. This also means the front motor mounts are being pushed up and the rear down. So I came up with a system of 5 vertical and 6 horizontal lag bolts to hold each motor mount, and I fabricated some "tee" style mounts out of aluminum plate.
Then I used two tubes of 3M 5200 to hold everything in place and I installed the mounts, they are shown below. Yes it is overkill and yes I spent too much pulling the motor, making the mounts etc but now I have piece of mind, at least when it comes to this (one of many) problem.
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